Antiphospholipid Syndrome 

Updated: Nov 24, 2020
Author: Suneel Movva, MD; Chief Editor: Herbert S Diamond, MD 


Practice Essentials

Antiphospholipid syndrome (APS) is an acquired autoimmune disorder that manifests clinically as recurrent venous or arterial thrombosis and/or fetal loss.[1] Characteristic laboratory abnormalities in APS include persistently elevated levels of antibodies directed against membrane anionic phospholipids (ie, anticardiolipin [aCL] antibody, antiphosphatidylserine) or their associated plasma proteins, predominantly beta-2 glycoprotein I (apolipoprotein H); or evidence of a circulating anticoagulant. See Presentation and Workup.

Multiple terms for APS exist. Unfortunately, some synonyms can be confusing. Lupus anticoagulant (LA) syndrome, for example, is misleading—first, because patients with APS may not necessarily have systemic lupus erythematosus (SLE), and second, because although LAs do have an anticoagulant effect in vitro, LA syndrome manifests clinically with thrombotic rather than hemorrhagic complications. In an attempt to avoid further confusion, APS is currently the preferred term for the clinical syndrome (as described below).

Some patients with APS have no evidence of any definable associated disease, while, in other patients, APS occurs in association with SLE or another rheumatic or autoimmune disorder. Traditionally, these have been referred to as primary or secondary APS, respectively. Currently, however, the preferred terminology is APS with or without associated rheumatic disease. Although antiphospholipid (aPL) antibodies are clinically linked to APS, whether they are involved in the pathogenesis or are an epiphenomenon is unclear. (Up to 5% of healthy individuals are known to have aPL antibodies.)

The development of aPL antibodies has been described in association with thrombosis in patients with COVID-19, and in a cohort study from France, lupus anticoagulant was detected in a large percentage of patients with severe COVID-19. However, it is not yet known whether the aPL antibodies in these patients play a role in COVID-19–associated thrombosis or merely represent an association.[2]

In general, treatment regimens for APS must be individualized according to the patient's current clinical status and history of thrombotic events. Asymptomatic individuals in whom blood test findings are positive do not require specific treatment. Prophylaxis is needed during surgery or hospitalization, as well as management of any associated autoimmune disease. Low-dose aspirin is used widely in this setting; although its effectiveness remains unproven. For thrombosis, perform full anticoagulation with intravenous or subcutaneous heparin followed by warfarin therapy. See Treatment.

For discussion of APS in children, see Pediatric Antiphospholipid Antibody Syndrome. For discussion of obstetric APS, see Antiphospholipid Syndrome and Pregnancy.


In APS, the homeostatic regulation of blood coagulation is altered; however, the mechanisms of thrombosis are not yet defined. One hypothesis postulates a defect in cellular apoptosis, which exposes membrane phospholipids to the binding of various plasma proteins, such as beta-2 glycoprotein I. Once bound, a phospholipid-protein complex is formed and a neoepitope is uncovered, which subsequently becomes the target of autoantibodies. Recent evidence suggests that oxidized beta-2 glycoprotein I is able to bind to and activate dendritic cells in a manner similar to activation triggered by Toll-like receptor 4 (TLR-4), which could amplify the production of autoantibodies.[1, 3]

Other proposed mechanisms for the hypercoagulable effect of aPL antibodies, which may or may not depend on beta-2 glycoprotein I, include the following:

  • Production of antibodies against coagulation factors, including prothrombin, protein C, protein S, and annexins

  • Activation of platelets to enhance endothelial adherence

  • Activation of vascular endothelium, which, in turn, facilitates the binding of platelets and monocytes

  • Reaction of antibodies to oxidized low-density lipoprotein, thus predisposing to atherosclerosis and myocardial infarction (MI)

Complement activation has been increasingly recognized as a possible significant role in the pathogenesis of APS. Emerging evidence from murine models suggests that APL-mediated complement activation may be a primary event in pregnancy loss.[3, 4]

Clinically, the series of events that leads to hypercoagulability and recurrent thrombosis can affect virtually any organ system, including the following:

  • Peripheral venous system (deep venous thrombosis [DVT])

  • Central nervous system (stroke, sinus thrombosis, seizures, chorea, reversible cerebral vasoconstriction syndrome)

  • Peripheral nervous system (peripheral neuropathy including Guillain–Barré syndrome)

  • Hematologic (thrombocytopenia, hemolytic anemia)

  • Obstetric (pregnancy loss, eclampsia)

  • Pulmonary (pulmonary embolism [PE], pulmonary hypertension)

  • Dermatologic (livedo reticularis, purpura, infarcts/ulceration)

  • Cardiac (Libman-Sacks valvulopathy, MI, diastolic dysfunction)

  • Ocular (amaurosis, retinal thrombosis)

  • Adrenal (infarction/hemorrhage)

  • Musculoskeletal (avascular necrosis of bone)

  • Renal (thrombotic microangiopathy)

The kidney is  a major target organ in APS. Nephropathy in APS is characterized by small-vessel vaso-occlusive lesions associated with fibrous intimal hyperplasia of interlobular arteries, recanalizing thrombi in arteries and arterioles, and focal atrophy.[5]

A “two-hit” theory has been proposed in which a second risk factor (age, hypertension, diabetes, obesity, smoking, pregnancy, surgery, other genetic hypercoagulable state) incites the thrombotic effects of aPL.[6]



United States

The actual frequency of APS in the general population is unknown. One to 5% of healthy individuals have aPL antibodies. It is estimated that the incidence of APS is approximately 5 cases per 100,000 persons per year, and the prevalence is approximately 40-50 cases per 100, 000 persons.[7] aCL antibodies tend to be found more frequently in elderly persons; thus, positive titer results should be interpreted with caution in this population. aPL antibodies are found in approximately 30-40% of patients with SLE, but only about 10% have APS.[8] Approximately half of APS cases are not associated with another rheumatic disease. In a study of 100 patients with confirmed venous thrombosis and no history of SLE, aCL antibodies were found in 24% and LA in 4%.

 aPL are positive in approximately 13% of patients with stroke, 11% with myocardial infarction, 9.5% of patients with deep vein thrombosis, and 6% of patients with pregnancy morbidity.[9]


International frequency is probably similar to US frequency.


APS may contribute to an increased frequency of stroke or MI, especially in younger individuals. Strokes may develop secondary to in situ thrombosis or embolization that originates from the valvular lesions of Libman-Sacks (sterile) endocarditis, which may be seen in patients with APS. Cardiac valvular disease may be severe enough to require valve replacement. Recurrent pulmonary emboli or thrombosis can lead to life-threatening pulmonary hypertension.

Catastrophic APS (CAPS) is a rare, serious, and often fatal manifestation characterized by multiorgan infarctions over a period of days to weeks. Mortality rates of 50% have been reported; however, with triple therapy (anticoagulation, corticosteroids, plasma exchange and/or intravenous immunoglobulin) data from an international registry showed a mortality rate of 28.6%.[10]

Late spontaneous fetal loss (second or third trimester) is common; however, it can occur at any time during pregnancy. Recurrent early fetal loss (< 10 weeks’ gestation) is also possible.

Race-, Sex-, and Age-related Demographics

No defined racial predominance for primary APS has been documented, although SLE is more common in African American and Hispanic populations.

A female predominance has been documented, particularly for secondary APS. This parallels the association of APS with SLE and other connective-tissue diseases, which also have a female predominance.

APS is more common in young to middle-aged adults; however, it also manifests in children and elderly people. Disease onset has been reported in children as young as 8 months. In an international registry of pediatric APS cases, patients without associated rheumatic disease were younger and had a higher frequency of arterial thrombotic events, whereas patients with associated rheumatic disease were older and had a higher frequency of venous thrombotic events associated with hematologic and skin manifestations.[11]




Antiphospholipid syndrome (APS) is a heterogenous disorder in terms of clinical manifestations and range of autoantibodies. In 2006, revised criteria for the diagnosis of APS were published in an international consensus statement.[12] At least one clinical criterion and one laboratory criterion (discussed further in Lab Studies) must be present for a patient to be classified as having APS.

The clinical criteria consist of vascular thrombosis and pregnancy morbidity. Vascular thrombosis is defined as one or more clinical episodes of arterial, venous, or small-vessel thrombosis in any tissue or organ confirmed by findings from imaging studies, Doppler studies, or histopathology (see Histologic Findings).

Thrombosis may involve the cerebral vascular system, coronary arteries, pulmonary system (emboli or thromboses), arterial or venous system in the extremities, hepatic veins, renal veins, ocular arteries or veins, or adrenal glands. Investigation is warranted if a history of deep venous thrombosis (DVT, pulmonary embolism (PE), acute ischemia, myocardial infarction (MI), or stroke (especially when recurrent) is present in a younger individual (males < 55 y; females < 65 y) or in the absence of other risk factors.

Pregnancy morbidity is defined as the following:

  • One or more late-term (>10 weeks' gestation) spontaneous abortions

  • One or more premature births of a morphologically healthy neonate at or before 34 weeks’ gestation because of severe preeclampsia or eclampsia or severe placental insufficiency

  • Three or more unexplained, consecutive, spontaneous abortions before 10 weeks’ gestation

Laboratory criteria include any of the following (see also Lab Studies):

  • Medium to high levels of immunoglobulin G (IgG) or immunoglobulin M (IgM) anticardiolipin (aCL) Anti–beta-2 glycoprotein I

  • Lupus anticoagulant on at least two occasions at least 12 weeks apart

Testing for novel antibodies not recognized in the 2006 criteria can be considered if clinical suspicion is high, although in select cases they may not be commercially available.

Other antiphospholipid (aPL)–associated clinical features recognized by the 2006 consensus statement but not included in the criteria include cardiac valve disease, livedo reticularis, thrombocytopenia, nephropathy, and neurologic manifestations.

Thus, history of any of the following should raise the examiner's suspicion for APS:

  • Thrombosis (eg, DVT/PE, MI, transient ischemic attack [TIA], or stroke, especially if recurrent, at an earlier age, or in the absence of other known risk factors)

  • Miscarriage (especially late trimester or recurrent) or premature birth

  • History of heart murmur or cardiac valvular vegetations

  • History of hematologic abnormalities, such as thrombocytopenia or hemolytic anemia

  • History of nephropathy

  • Nonthrombotic neurologic symptoms, such as migraine headaches, chorea, seizures, transverse myelitis, Guillain-Barré syndrome, or dementia (rare)

  • Unexplained adrenal insufficiency

  • Avascular necrosis of bone in the absence of other risk factors

  • Pulmonary hypertension


Cutaneous manifestations include the following:

  • Livedo reticularis (see image below)

    Antiphospholipid syndrome. Livedo reticularis. Antiphospholipid syndrome. Livedo reticularis.
  • Superficial thrombophlebitis

  • Leg ulcers

  • Painful purpura

  • Splinter hemorrhages

Venous thrombosis–related findings include the following:

  • Leg swelling (DVT)

  • Ascites (Budd-Chiari syndrome)

  • Tachypnea (pulmonary embolism)

  • Peripheral edema (renal vein thrombosis)

  • Abnormal funduscopic examination results (retinal vein thrombosis)

Arterial thrombosis–related findings include the following:

  • Abnormal neurologic examination results (eg, stroke)

  • Digital ulcers

  • Gangrene of distal extremities (see image below)

    Antiphospholipid syndrome. Arterial thrombosis res Antiphospholipid syndrome. Arterial thrombosis resulting in ischemia and necrosis of the foot.
  • Signs of myocardial infarction

  • Heart murmur (frequently aortic) or mitral insufficiency (Libman-Sacks endocarditis)

  • Abnormal funduscopic examination results (retinal artery occlusion)


APS is an autoimmune disorder of unknown cause. The search for possible triggers has uncovered a wide array of associated autoimmune or rheumatic diseases, infections, and drugs that are associated with the LA or aCL antibodies. These associations may ultimately provide a clue to the etiology of APS. A considerable percentage of persons with certain autoimmune or rheumatic diseases also have aPL antibodies.

Common autoimmune or rheumatic diseases and the percentage of affected patients with aPL antibodies are as follows (note that these represent percentages of patients with aPL antibodies, rather than the clinical syndrome of APS[13] ):

  • SLE - 25-50%
  • Sjögren syndrome - 42%
  • Rheumatoid arthritis - 33%
  • Autoimmune thrombocytopenic purpura - 30%
  • Autoimmune hemolytic anemia - Unknown
  • Psoriatic arthritis - 28%
  • Systemic sclerosis - 25%
  • Mixed connective-tissue disease - 22%
  • Polymyalgia rheumatica or giant cell arteritis - 20%
  • Behçet syndrome - 20%

Infections associated with APS include the following[14] :

  • Syphilis
  • Hepatitis C 
  • HIV infection
  • Human T-cell lymphotrophic virus type 1 infection
  • Malaria
  • Bacterial septicemia

Drugs associated with APS include the following:

  • Cardiac - Procainamide, quinidine, propranolol, hydralazine
  • Neuroleptic or psychiatric - Phenytoin, chlorpromazine
  • Other - Interferon alfa, quinine, amoxicillin

In addition, certain vaccines have been associated with APS. For example, vaccination with tetanus toxoid may trigger the formation of antibodies that cross-react with βbeta-2 glycoprotein I, due to molecular mimicry between the two molecules.[15]

 Genetic predisposition may be involved, as follows:

  • Relatives of persons with known APS are more likely to have aPL antibodies. One study showed a 33% frequency.
  • An association has been found between aCL antibody and carriage of certain HLA genes, including DRw53, DR7 (mostly in people of Hispanic origin), and DR4 (mostly in whites).


Diagnostic Considerations

Other problems to be considered in the differential diagnosis include the following:

  • Hypercoagulable state: Malignancy, oral contraceptive use and hormone replacement therapy, homocystinemia, antithrombin III deficiency, protein C or S deficiency, factor V Leiden mutation, prothrombin A20210 mutation, antiprothrombin antibodies

  • Atherosclerotic vascular disease, including multiple cholesterol emboli syndrome

  • Systemic necrotizing vasculitis

Differential Diagnoses



Laboratory Studies

The hallmark result from laboratory tests that defines antiphospholipid syndrome (APS) is the presence of antiphospholipid (aPL) antibodies or abnormalities in phospholipid-dependent tests of coagulation. In addition to the clinical criteria listed in History, at least one of the following laboratory criteria is necessary for the classification of APS:

  • Presence of lupus anticoagulant (LA) in plasma on two or more occasions at least 12 weeks apart (see below)

  • Presence of moderate to high levels of anticardiolipin (aCL) (IgG or IgM) in serum or plasma (ie, > 40 IgG phospholipid units (GPL)/mL or IgM phospholipid units (MPL)/mL or > 99th percentile) on two or more occasions at least 12 weeks apart

  • Presence of moderate to high levels of anti–beta-2 glycoprotein I antibodies (IgG or IgM) in serum or plasma (> 99th percentile) on two or more occasions at least 12 weeks apart

aCL antibodies react primarily to membrane phospholipids, such as cardiolipin and phosphatidylserine. Of the 3 known isotypes of aCL (ie, IgG, IgM, immunoglobulin A [IgA]), IgG correlates most strongly with thrombotic events. Cardiolipin is the dominant antigen used in most serologic tests for syphilis; consequently, these patients may have a false-positive test result for syphilis.

The literature suggests that an abnormal LA finding is the laboratory test result that confers the strongest risk for thrombosis.[6, 16] LA is directed against plasma coagulation molecules. In vitro, this interaction results in the paradoxical prolongation of clotting assays, such as activated partial thromboplastin time (aPTT), kaolin clotting time, and dilute Russell viper venom time (DRVVT). The presence of LA is confirmed by mixing normal platelet-poor plasma with the patient's plasma. If a clotting factor is deficient, the addition of normal plasma corrects the prolonged clotting time. If the clotting time does not normalize during mixing studies, an inhibitor is present; the absence of a specific clotting factor inhibitor confirms that a LA is present.

Currently, there is much investigation into risk-stratifying patients based on aPL profile, aPL titers, associated autoimmune disease, and other cardiovascular risk factors. "Triple-positive" patients (LA, anti-beta-2 glycoprotein antibodies, AC antibodies) are at highest risk for thrombosis or abnormal pregnancy, and possibly for recurrence.[6] Standardized scoring systems such as the Global Antiphospholipid Syndrome Score (GAPSS) are being developed.

Patients with APS may have one or more abnormal results from these laboratory tests; the following laboratory tests should be considered in a patient suspected of having APS:

  • aCL antibodies (IgG, IgM)
  • Anti–beta-2 glycoprotein I antibodies (IgG, IgM)
  • Activated partial thromboplastin time (aPTT)
  • LA tests such as DRVVT (A threshold of approximately 1.6 for the DRVVT ratio has been recommended for helping discriminate APS from non-APS. [17] )
  • Serologic test for syphilis (false-positive result)
  • CBC count (thrombocytopenia, hemolytic anemia)

A study of 97 pregnancies in women with a past history of APS concluded that  aPL antibodiy profiling to determine obstetric risk is best performed during the first trimester of pregnancy. Latino et al reported that risk categorization performed during pregnancy  predicted pregnancy outcome more accurately than categorization performed before pregnancy (91.8% vs 82.5%, respectively).[18]

Thrombocytopenia is fairly common in persons with APS (22% at presentation, 30% cumulatively) and is therefore associated with paradoxical thrombosis. However, patients with platelet counts of less than 50,000/µL may have an increased risk of bleeding. Hemolytic anemia has been well described in patients with APS and is associated with the presence of IgM aCL antibodies.

A low antinuclear antibody level may be present and does not necessarily imply coexisting SLE.

Additional antibodies directed against phospholipid/phospholipid-protein complexes for which testing may be useful in selected cases (seronegative APS, because they are not part of the 2006 consensus criteria) include the following[19, 20, 9] :

  • IgA aCL
  • IgA beta-2 glycoprotein I
  • Anti-phosphatidylserine antibodies
  • Anti-phosphatidylethanolamine antibodies
  • Anti-prothrombin antibodies
  • Antibodies against the phosphatidylserine-prothrombin complex

For further information, see Antiphospholipid Antibodies.

Imaging Studies

Imaging studies are helpful for confirming a thrombotic event. Examples are the use of computed tomography (CT) or magnetic resonance imaging (MRI) scans of the following:

  • Brain (for stroke)
  • Chest (for pulmonary embolism)
  • Abdomen (for Budd-Chiari syndrome)

Doppler ultrasound studies are recommended for possible detection of DVT.

Two-dimensional echocardiography findings may demonstrate asymptomatic valve thickening, vegetations, or valvular insufficiency; aortic or mitral insufficiency is the most common valvular defect found in persons with Libman-Sacks endocarditis.

Histologic Findings

Unlike inflammatory autoimmune diseases, histologic studies of skin or other involved tissue reveal a noninflammatory bland thrombosis with no signs of perivascular inflammation or leukocytoclastic vasculitis. Similarly, biopsy samples from affected kidneys demonstrate glomerular and small arterial microthrombi.



Medical Care

Patients with antiphospholipid syndrome (APS) may be evaluated in an outpatient setting. Inpatient evaluation is required if the patient presents with a significant clinical event. Patients with catastrophic APS (CAPS) require intense observation and treatment, often in an intensive care unit.

In general, treatment regimens for APS must be individualized according to the patient's current clinical status and history of thrombotic events. Asymptomatic individuals in whom blood test findings are positive do not require specific treatment.

Prophylactic therapy

Eliminate other risk factors, such as oral contraceptives, smoking, hypertension, or hyperlipidemia. Prophylaxis is needed during surgery or hospitalization, as well as management of any associated autoimmune disease.

Low-dose aspirin is used widely in this setting; however, the effectiveness of low-dose aspirin as primary prevention for APS remains unproven[9] . Clopidogrel has anecdotally been reported to be helpful in persons with APS and may be useful in patients allergic to aspirin.

In patients with systemic lupus erythematosus (SLE), consider hydroxychloroquine, which may have intrinsic antithrombotic properties.

Consider the use of statins, especially in patients with hyperlipidemia.

Treatment of thrombosis

Perform full anticoagulation with intravenous or subcutaneous heparin followed by warfarin therapy. Based on the most recent evidence, a reasonable target for the international normalized ratio (INR) is 2.0-3.0 for venous thrombosis and 3.0 for arterial thrombosis. Patients with recurrent thrombotic events may require an INR of 3.0-4.0. For severe or refractory cases, a combination of warfarin and aspirin may be used. Treatment for significant thrombotic events in patients with APS is generally lifelong.

Direct oral anticoagulants (ie, direct thrombin inhibitors and factor Xa inhibitors such as rivaroxaban) have been used in patients who are warfarin intolerant/allergic or have poor anticoagulant control.[9, 21] However, studies of these agents in APS patients have largely proved disappointing.

In the Rivaroxaban for Antiphospholipid Syndrome (RAPS) trial—a controlled, open-label, phase II/III non-inferiority trial in 116 APS patients—the percentage change in endogenous thrombin potential at 42 days for rivaroxaban was inferior to that of warfarin. However, because no thromboembolic events occurred over the 210‐day follow‐up in either group, the investigators concluded that rivaroxaban might be an effective and safe alternative in patients with APS and previous venous thromboembolism (VTE).[22]

A cohort study in 176 APS patients followed for a median of 51 months reported an increased risk of recurrent thromboembolic events and recurrent VTE alone in patients receiving direct oral anticoagulants compared with those receiving warfarin. No differences were found between rivaroxaban and apixaban or among single-positive, double-positive, and triple-positive APS.[23]

The phase III Rivaroxaban in Thrombotic Antiphospholipid Syndrome (TRAPS) trial, which was conducted in high-risk APS patients triple-positive for lupus anticoagulant, anti-cardiolipin, and anti-β2-glycoprotein I antibodies of the same isotype, was terminated prematurely after the enrollment of 120 patients because of an excess rate of arterial thromboembolic events in patients on rivaroxaban: 12% (4 ischemic strokes and 3 myocardial infarctions) versus 0% in patients on warfarin, after 569 days’ follow‐up.[24]

In May 2019, the European Medicines Agency (EMA) issued a guidance statement recommending against the use of direct-acting oral anticoagulants (including rivaroxaban, apixaban, edoxaban, and dabigatran etexilate) for patients with a history of thrombosis who are diagnosed with APS, in particular those that are triple positive. This poses a challenge for clinicians, however, because current guidelines recommend direct oral anticoagulants for treatment of VTE. A proportion of patients with a first unprovoked VTE will have antiphospholipid antibodies, and some of those will have APS. However, when a patient presents with unprovoked VTE it is impossible to know whether APS is present, as the diagnosis of APS requires testing on two or more occasions at least 12 weeks apart.[25]

Rituximab can be considered for recurrent thrombosis despite adequate anticoagulation. A nonrandomized prospective study showed rituximab to be effective for noncriteria aPL manifestations (ie, thrombocytopenia and skin ulcers).[6]

Obstetric considerations

Guidelines from the American College of Obstetricians and Gynecologists (based primarily on consensus and expert opinion [level C]) recommend that women with APS who have a history of thrombosis in previous pregnancies receive prophylactic anticoagulation during pregnancy and for 6 weeks postpartum. For women with APS who have no history of thrombosis, the guidelines suggest that clinical surveillance or prophylactic heparin use antepartum, along with 6 weeks of postpartum anticoagulation, may be warranted.[26]

Prophylaxis during pregnancy is provided with subcutaneous heparin (preferably low–molecular-weight heparin [LMWH]) and low-dose aspirin. Therapy is withheld at the time of delivery and is restarted after delivery, continuing for 6-12 weeks, or long-term in patients with a history of thrombosis.

The European League Against Rheumatism (EULAR) has published recommendations for women's health and the management of family planning, assisted reproduction, pregnancy, and menopause in patients with SLE and/or APS. EULAR also recommends prophylactic heparin and low-dose aspirin during pregnancy for patients with APS.[27]

Warfarin is contraindicated in pregnancy. Breastfeeding women may use heparin and warfarin.

Corticosteroids have not been proven effective for persons with primary APS, and they have been shown to increase maternal morbidity and fetal prematurity rates.

Unfortunately, current treatment fails to prevent complications in 20 to 30% of APS pregnancies.[28, 29] Retrospective clinical studies suggest that treatment with hydroxychloroquine may help prevent pregnancy complications in women with aPL and APS, and this strategy is currently being studied in a randomized controlled multicenter trial.[29]

See also Antiphospholipid Syndrome and Pregnancy.

Catastrophic antiphospholipid syndrome

Patients with CAPS are generally very ill, often with active SLE.[30] The condition is too rare to support clinical trials, but improved mortality has been reported with triple therapy consisting of anticoagulation, corticosteroids, and plasma exchange and/or intravenous immunoglobulin.[10] In addition, attention should be paid to associated disorders (eg, infection, SLE).  Cyclophosphamide has been used in cases associated with SLE, although its use in first-trimester pregnancy increases risk of fetal loss.[27, 30] In refractory or relapsing cases, rituximab and eculizumab have been used.[30]


Surgical Care

Placement of an inferior vena cava (IVC) filter may be considered in patients with APS who require cessation of anticoagulation or who continue to experience thrombotic complications despite maximal anticoagulation. Experts recommend avoiding IVC filters in the setting of acute APS, due to reports of adverse events including IVC thrombosis and pulmonary embolus. Baig et al evaluated the use of retrievable IVC filters in five patients with APS and concluded that retrievable IVC filters can be safely placed and removed in such patients, even during anticoagulation.[31]  


Consultations may include the following:

  • Rheumatologist
  • Hematologist
  • Neurologist, cardiologist, pulmonologist, hepatologist, ophthalmologist (depending on clinical presentation)
  • Obstetrician with experience in high-risk pregnancies


Medication Summary

In deciding whether to initiate anticoagulant prophylaxis for patients with antiphospholipid syndrome (APS), the benefits of these agents must be weighed carefully against their significant risks. Life-long treatment with warfarin (see Treatment) is standard for patients who experience recurrent thrombotic events.

Heparin therapy may be administered in several regimens, as follows:

  • Thrombotic events are initially treated with intravenous infusion of unfractionated heparin or therapeutic doses of subcutaneous low molecular weight heparin (LMWH) and low-dose aspirin.

  • Subcutaneous LMWH (enoxaparin [Lovenox]) may also be used for obstetric or thrombosis prophylaxis. Lower doses (20-40 mg/d SC) are used to prevent fetal loss, while higher doses (1 mg/kg q12h or 1.5 mg/kg/d) are used for thrombosis prophylaxis in patients (pregnant or nonpregnant) who have had prior thrombotic events.

Patients who require heparin administration throughout pregnancy should receive calcium and vitamin D supplementation to help avoid heparin-induced osteoporosis. When monitoring heparin therapy, note that the activated partial thromboplastin time (aPTT) may be unreliable in the presence of circulating antiphospholipid (aPL) antibodies with a baseline elevated aPTT. In this case, factor Xa may be helpful.

Hydroxychloroquine has antithrombotic properties and may be considered in the prophylactic treatment of a patient with SLE and a positive  aPL antibody test result.[21] The use of hydroxychloroquine and intravenous immunoglobulin (IVIG) has been associated with good outcomes in pregnant women with APS who develop recurrent episodes of thrombosis or catastrophic APS (CAPS) despite receiving adequate antithrombotic treatment.[32]

In addition to full anticoagulation, plasma exchange and corticosteroids are generally used in the treatment of CAPS. IVIG or cyclophosphamide may be considered in selected patients with CAPS. However, cyclophosphamide increases the risk of first-trimester fetal loss, so its use in pregnant women should be reserved for severe, life-threatening or refractory manifestations during the second or third trimester.[27]

Statins have been suggested to have potential antithrombotic effects. Statins are recommended for APS patients with hyperlipidemia and, possibly, in aPL patients with recurrent thromboses despite adequate anticoagulation.[21]

Rituximab has shown benefit in controlling severe thrombocytopenia, skin ulcers, and cognitive dysfunction that can be associated with APS.[21]

Case reports have described the use of eculizumab, a humanized monoclonal antibody against C5 complement protein, in CAPS, and in aPL-positive patients undergoing renal transplantation.[33]


Class Summary

Standard therapy for thrombosis commonly consists of intravenous heparin followed by warfarin. Treatment of a pregnant patient with a history of recurrent fetal loss is controversial but generally includes subcutaneous heparin and aspirin.

Warfarin (Coumadin)

Interferes with hepatic synthesis of vitamin K–dependent coagulation factors. Long-term warfarin is DOC for APS in patients with recurrent thrombotic events. Titrated dose suggested to maintain INR in therapeutic range (see above).

Enoxaparin (Lovenox)

LMWH. Most experience; other LMWH preparations available.


Used in inpatient settings as continuous infusion during conversion to warfarin therapy until a therapeutic INR is achieved. May be administered SC as substitute for warfarin during attempted pregnancy or for temporary anticoagulation during warfarin loading in outpatient setting.

Aspirin (Anacin 81, Ascriptin, Bayer Aspirin)

Although not proven effective when used alone, most clinicians use aspirin with SC heparin in pregnant patients with APS. Begin aspirin as soon as conception is attempted.


Class Summary

As prophylactic therapy, these agents may have an additional anticoagulant effect in patients with SLE.

Hydroxychloroquine (Plaquenil)

Most common antimalarial used in APS, mostly because of excellent safety profile.

Immunosuppressive agents

Class Summary

Consider immunosuppressive agents in select cases (eg, refractory APS, CAPS).

Cyclophosphamide (Cytoxan, Neosar)

Chemically related to nitrogen mustards. As an alkylating agent, mechanism of action of active metabolites may involve cross-linking of DNA, which may interfere with growth of normal and neoplastic cells. Has not been shown to be effective in APS.


Class Summary

In selected cases with specific nonthrombotic autoimmune manifestations (eg, clinically significant thrombocytopenia), corticosteroids may be considered.

Prednisone (Deltasone, Orasone, Sterapred)

Immunosuppressant for treatment of autoimmune disorders. May decrease inflammation by reversing increased capillary permeability and suppressing PMN activity. Useful in treating cytopenias.

Immunomodulatory therapy agents

Class Summary

These agents interfere with processes that promote immune reactions resulting from diverse stimuli.

Intravenous immune globulins, 5% (Gammagard, Gamimune)

Following features may be relevant to efficacy: neutralization of circulating myelin antibodies through antiidiotypic antibodies, down-regulation of proinflammatory cytokines (including IFN-gamma), blockade of Fc receptors on macrophages, suppression of helper/inducer T and B cells and augmentation of suppressor T cells, blockade of the complement cascade, promotion of remyelination, and 10% increase in CSF IgG. May be effective in APS.



Further Outpatient Care

Subsequent outpatient care includes the following:

  • Carefully monitor medication doses and the INR if applicable.
  • Closely observe the patient for clinical events.
  • Ensure the care of any underlying connective-tissue disease.

Inpatient & Outpatient Medications

The suggested medications include heparin, warfarin, aspirin, and, in selected cases, hydroxychloroquine, intravenous immunoglobulin, and corticosteroids.

Corticosteroids are rarely used for the treatment of recurrent fetal loss because of the increased risk of maternal morbidity. Generally, the use of corticosteroids is reserved for specific nonthrombotic manifestations, such as associated thrombocytopenia, autoimmune hemolytic anemia, or the treatment of an underlying connective-tissue disease.

Prescribe antihypertensive drugs when necessary.

Administer antihyperlipidemic agents including statins when appropriate.


When treating seriously ill patients with catastrophic APS, transfer the patient to a setting where plasma exchange can be performed or where intravenous immunoglobulin or cyclophosphamide can be administered if needed.


Instruct the patient to avoid smoking.

Inform the patient to avoid oral contraceptives or estrogen replacement therapy.

Ensure that the patient avoids any prolonged immobilization.


Permanent functional disability or death can occur at a relatively young age. Complications may include the following:

  • Stroke
  • Myocardial infarction
  • Pulmonary hypertension
  • Renal failure [34]


With appropriate medication and lifestyle modifications, most individuals with primary antiphospholipid syndrome (APS) lead normal healthy lives. However, subsets of patients continue to have thrombotic events despite aggressive therapies. In these patients and in patients with catastrophic APS, the disease course can be devastating, often leading to significant morbidity or early death.

In large European cohort studies, 10-year survival is approximately 90-94%.[35]

A retrospective study suggested that hypertension or medium-to-high titers of IgG anticardiolipin antibody are risk factors for a first thrombotic event in asymptomatic patients with antiphospholipid (aPL) antibodies.[36] Primary prophylaxis against thrombosis appears to offer significant protection in such cases. Annual incidence of first thrombosis is approximately 0-5% in patients with a positive aPL test without previous thrombosis.[9]

Patients with secondary APS carry a prognosis similar to that of patients with primary APS; in the former, however, morbidity and mortality may also be influenced by these patients' underlying autoimmune or rheumatic condition. In patients with SLE and APS, aPL antibodies have been associated with neuropsychiatric disease and have been recognized as a major predictor of irreversible organ damage.

Women with aPL antibodies who experience recurrent miscarriages may have favorable prognoses in subsequent pregnancies if treated with aspirin and heparin.

Patient Education

Patient education may include the following:

  • Stress the importance of early recognition of a possible clinical event.
  • Instruct patients taking warfarin to avoid sports with excessive contact.
  • Instruct patients taking warfarin to avoid excessive consumption of foods that contain vitamin K. [37]
  • Limit activity in patients with acute DVT.
  • Instruct the patient to avoid prolonged immobilization.
  • Discuss the importance of planned pregnancies so that long-term warfarin can be switched to aspirin and heparin before pregnancy is attempted.
  • Stress the importance of minimizing modifiable risk factors in primary prevention of aPL-positive patients with no history of thrombosis.

For patient education information, see Blood Clot in the Legs.


Questions & Answers


What is antiphospholipid syndrome (APS)?

What are the subtypes of antiphospholipid syndrome (APS)?

What are the treatment options for antiphospholipid syndrome (APS)?

What is the "two-hit" theory of the pathogenesis of antiphospholipid syndrome (APS)?

What is the pathophysiology of antiphospholipid syndrome (APS)?

What is the role of complement activation in the pathogenesis of antiphospholipid syndrome (APS)?

Which organ systems can be affected by antiphospholipid syndrome (APS)?

What is a major target organ in antiphospholipid syndrome (APS)?

What is the prevalence of antiphospholipid syndrome (APS)?

What is the mortality and morbidity of antiphospholipid syndrome (APS)?

What are the racial predilections of antiphospholipid syndrome (APS)?

How does the prevalence of antiphospholipid syndrome (APS) vary by sex?

How does the prevalence of antiphospholipid syndrome (APS) vary by age?


How is antiphospholipid syndrome (APS) diagnosed?

What are the clinical criteria for diagnosis of antiphospholipid syndrome (APS)?

What are the lab criteria for diagnosis of antiphospholipid syndrome (APS)?

Which clinical features of antiphospholipid syndrome (APS) are not included in the diagnostic criteria?

What history suggests antiphospholipid syndrome (APS)?

What are the cutaneous manifestations of antiphospholipid syndrome (APS)?

Which venous thrombosis-related findings are characteristic of antiphospholipid syndrome (APS)?

Which arterial thrombosis-related findings are characteristic of antiphospholipid syndrome (APS)?

What causes antiphospholipid syndrome (APS)?

What diseases and conditions are associated with antiphospholipid syndrome (APS)?


Which conditions should be included in the differential diagnoses for antiphospholipid syndrome (APS)?

What are the differential diagnoses for Antiphospholipid Syndrome?


What is the role of lab tests in the diagnosis of antiphospholipid syndrome (APS)?

What is the role of aCL antibody testing in the diagnosis of antiphospholipid syndrome (APS)?

Which lab tests may be helpful in the workup of antiphospholipid syndrome (APS)?

What is the prevalence of thrombocytopenia in antiphospholipid syndrome (APS)?

What antinuclear antibody levels may be present in patients with antiphospholipid syndrome (APS)?

Which antibody testing may be useful in the diagnosis of antiphospholipid syndrome (APS)?

What is the role of imaging studies in the workup of antiphospholipid syndrome (APS)?

What is the role of Doppler ultrasound in the workup of antiphospholipid syndrome (APS)?

What is the role of two-dimensional echocardiography findings in the workup of antiphospholipid syndrome (APS)?

What are histologic findings characteristic of antiphospholipid syndrome (APS)?


When is inpatient evaluation indicated for antiphospholipid syndrome (APS)?

What are the treatment options for antiphospholipid syndrome (APS)?

When is prophylactic therapy indicated for antiphospholipid syndrome (APS)?

How is thrombosis in antiphospholipid syndrome (APS) treated?

What are the guidelines for antiphospholipid syndrome (APS) prophylaxis during pregnancy?

What are the treatment options for catastrophic antiphospholipid syndrome (APS)?

When is surgical care indicated in the treatment of antiphospholipid syndrome (APS)?

Which specialist consultations are needed for the treatment of antiphospholipid syndrome (APS)?


What are considerations before initiation of anticoagulant prophylaxis for antiphospholipid syndrome (APS)?

What are the options for administration of heparin therapy for antiphospholipid syndrome (APS)?

What is the role of hydroxychloroquine in the treatment of antiphospholipid syndrome (APS)?

What are the medications used to treat catastrophic antiphospholipid syndrome (APS)?

What is the indication for statins for the treatment of antiphospholipid syndrome (APS)?

What is the role of rituximab in the treatment of antiphospholipid syndrome (APS)?

What is the role of eculizumab in the treatment of antiphospholipid syndrome (APS)?

Which medications in the drug class Immunomodulatory therapy agents are used in the treatment of Antiphospholipid Syndrome?

Which medications in the drug class Corticosteroids are used in the treatment of Antiphospholipid Syndrome?

Which medications in the drug class Immunosuppressive agents are used in the treatment of Antiphospholipid Syndrome?

Which medications in the drug class Antimalarials are used in the treatment of Antiphospholipid Syndrome?

Which medications in the drug class Anticoagulants are used in the treatment of Antiphospholipid Syndrome?


What monitoring is needed following treatment of antiphospholipid syndrome (APS)?

Which medications are used in the treatment of antiphospholipid syndrome (APS)?

When is transfer indicated for patients with antiphospholipid syndrome (APS)?

How is antiphospholipid syndrome (APS) prevented?

What are possible complications of antiphospholipid syndrome (APS)?

What is the prognosis of antiphospholipid syndrome (APS)?

What information about antiphospholipid syndrome (APS) should patients receive?